The invention relates to an apparatus for the longitudinal splitting of pipes which are laid underground and are made in particular from ductile materials, such as steel pipes, centrifugally cast pipes made from cast iron containing spheroidal graphite, and plastic pipes.
The trenchless initial laying of pipelines underground and the destructive replacement of underground pipelines have become increasingly popular in practice in recent decades. This requires automatically driven and/or pulled equipment which can be equipped with tools for destroying a pipeline which is to be replaced. The destruction of brittle pipes generally does not present any particular problems, since such pipes break up and the fragments can be displaced laterally into the earth or can be conveyed away.
By contrast, the destructive replacement of pipes made from tough materials, such as steel pipes, cast steel pipes and plastic pipes, which owing to their toughness cannot be broken into fragments, presents greater difficulty. In these cases, destruction by cutting is recommended, but even this method presents problems in the case of socket pipes or pipes which have been provided with repair fittings, owing to the high friction forces and the high cutting forces which are required in order for these pipes to be cut open.
U.S. Pat. No. 5,439,320 has already disclosed a static method in which a pipe cutter, in the form of a frame equipped with two cutting wheels, is pulled through the pipe which is to be destroyed with the aid of a pipe linkage. A double cone, the maximum diameter of which may be larger than the internal diameter of the pipe, is arranged in the frame, between the two cutting wheels. This double cone is used to guide the implement inside the old pipe and, at the same time, to bend open the pipe which has been slit by the cutting wheel which is situated in front of it in the direction of movement, while the cutting wheel which is situated behind the double cone is arranged in the frame in such a way that it projects radially beyond the other cutting wheel and is therefore able to cut open a socket joint by dint of its external diameter being larger than the pipe; in doing so, it follows a groove which has already been created in the area of the socket joint by the first cutting wheel. In addition, a conical expander head is screwed to the rear end of the frame, which expander head expands the longitudinally slit pipe further and, at the same time, pulls in a new pipe.
A drawback of this appliance is the considerable wall friction between the guide cone and the pipe wall, which not only requires high pulling forces but also, in the case of very dirty or partly blocked pipes, may lead to the appliance becoming jammed. An appliance which is known from U.S. Pat. No. 4,903,406, in which a cutting wheel is arranged in a frame between two rotatably mounted support wheels, avoids such skin friction. The frame is screwed, on the one hand, to a pull linkage and, on the other hand, to an expander cone, which is followed by a follower pipe. This screw connection is time-consuming and may be difficult if the screw threads are dirty or damaged.
Since the support wheels are arranged at a relatively great distance from one another, the frame is comparatively long and, in view of the comparatively great distance between the cutting-wheel axle and the support-wheel axles, is subject to considerable flexural forces.
The invention is based on the object of providing a pipe cutter or pipe breaker which is of simple design, is able to withstand high loads and can be connected to a linkage in a simple manner.
The solution to this problem is an apparatus having a carriage, in which in each case at least one rotatable cutting wheel for the longitudinal splitting, in particular longitudinal slitting, of a pipe and at least one support roller are arranged above one another, and which is connected in a form-fitting manner to a pull and/or push linkage. The term cutting wheels also encompasses wheels which break open the pipe wall.
The form-fitting connection can be achieved with the aid of a plug-together connection in which, for example, a base of the carriage engages behind a shoulder on the linkage or in a complementary opening, preferably a rectangular window, in the linkage. In the base, the support roller may preferably be mounted vertically beneath the cutting roller, resulting in an extremely compact and stable connection between the carriage and the window, which is, for example, frame-like, with the cutting wheel arranged above it.
The stability of the carriage/linkage system is increased still further if extension arms are arranged on both sides of the cutting wheel or of a plurality of cutting wheels and bear against the linkage. This results in a high anti-tipping security even when the carriage with the cutting wheel is supported on only a single roller.
A frame-like window and a correspondingly contoured base also prevent the cutting wheel from rotating about an axis which is perpendicular to the linkage and therefore also prevent the cutting wheel from becoming trapped in the slit which it has created. The cutting wheel therefore moves in a straight line and with correspondingly little friction from the pipe wall or the slit which the cutting wheel has created.
The carriage may also be provided with a plurality of cutting wheels which are arranged one behind the other and at staggered heights, each of which cutting wheels performs a particular function. For example, the front wheel, as seen in the direction of movement, can be used to cut open the pipe wall, while the following cutting wheel is arranged in such a way that it projects radially beyond the front cutting wheel and is therefore able to cut open a pipe socket joint. A third cutting wheel which projects radially beyond both the cutting wheels arranged in front of it is then responsible for cutting open or fully cutting open heavy repair fittings or sleeves which surround the pipe.
If a plurality of cutting wheels are used, it is not necessary for each cutting wheel to be assigned a support roller, although this is advantageous for static reasons.
The cutting carriage may be connected to a following expander member, with the aid of which the longitudinally split pipe is spread or bent open. The expander member and/or the cutting carriage may also be provided with blade cutters. In this way, it is possible for even relatively old pipelines, which often contain sections made from different materials, to be split in the longitudinal direction.
Furthermore, it is also possible to arrange a plurality of cutting carriages one behind the another and to connect them to one another or in each case to the linkage.
The cutting wheels and/or support rollers are made easy to install and remove if they are arranged on separate T-shaped plug-in pins which are held in situ by the frame of the window in the linkage in which the base having the plug-in pins is arranged.
In order to keep the pulling force which is required for longitudinal splitting at a low level, the cutting wheel may be contoured in the form of a circular saw blade, i.e. may have teeth whose backs are designed as cutters and cut through the pipe wall by levering it up from the inside. The eccentric action of the teeth means that the forces which act on the pipe wall are very high, so that the available pulling force is optimally exploited or can be lower than if a circular blade is used. This is of enormous importance particularly where there are strong repair sleeves. If the cutting carriage is equipped with a toothed wheel, a tooth comes to bear against the end side of the pipeline. If this cutting carriage is then pulled or pushed through the pipeline, the cutting roller must inevitably rotate. As a result of this forced rotation of the cutting roller, the following cutting tooth then rotates so as to cut or break into the pipe wall, thus creating the start of a slit.
The linkage which accommodates the cutting carriage is advantageously connected to an expander member which may be arranged on a pulling head. This pulling head may furthermore bear a support sleeve and may be connected to a follower pipe.
The linkage advantageously comprises ladder sections in which the side members and the rungs form windows into which a correspondingly dimensioned base of the cutting-wheel carriage can be fitted without difficulties. In this case, a special securing means for the plug connection is not absolutely necessary, since the wall of the pipeline which has been laid underground holds the linkage and the cutting-wheel carriage together.
Such a linkage with a push-pull drive for its stepwise movement through an underground pipe is described in German Patent 196 08 980, the content of which is to be regarded as part of this description.
A method in which, starting from a start shaft, a linkage is pushed through the pipeline until it reaches a target shaft, where the linkage is provided with a cutting appliance, for example a cutting appliance with a cutter which is directed downward, and, together with a following expander member and a follower pipe, is moved back to the target shaft, is preferably suitable for the longitudinal splitting of a pipeline which is laid underground and for pulling in a new pipe.